69 lines
2.0 KiB
Perl
69 lines
2.0 KiB
Perl
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package filetest;
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=head1 NAME
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filetest - Perl pragma to control the filetest permission operators
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=head1 SYNOPSIS
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$can_perhaps_read = -r "file"; # use the mode bits
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{
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use filetest 'access'; # intuit harder
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$can_really_read = -r "file";
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}
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$can_perhaps_read = -r "file"; # use the mode bits again
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=head1 DESCRIPTION
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This pragma tells the compiler to change the behaviour of the filetest
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permissions operators, the C<-r> C<-w> C<-x> C<-R> C<-W> C<-X>
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(see L<perlfunc>).
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The default behaviour to use the mode bits as returned by the stat()
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family of calls. This, however, may not be the right thing to do if
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for example various ACL (access control lists) schemes are in use.
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For such environments, C<use filetest> may help the permission
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operators to return results more consistent with other tools.
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Each "use filetest" or "no filetest" affects statements to the end of
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the enclosing block.
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There may be a slight performance decrease in the filetests
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when C<use filetest> is in effect, because in some systems
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the extended functionality needs to be emulated.
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B<NOTE>: using the file tests for security purposes is a lost cause
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from the start: there is a window open for race conditions (who is to
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say that the permissions will not change between the test and the real
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operation?). Therefore if you are serious about security, just try
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the real operation and test for its success. Think atomicity.
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=head2 subpragma access
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Currently only one subpragma, C<access> is implemented. It enables
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(or disables) the use of access() or similar system calls. This
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extended filetest functionality is used only when the argument of the
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operators is a filename, not when it is a filehandle.
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=cut
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$filetest::hint_bits = 0x00400000;
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sub import {
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if ( $_[1] eq 'access' ) {
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$^H |= $filetest::hint_bits;
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} else {
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die "filetest: the only implemented subpragma is 'access'.\n";
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}
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}
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sub unimport {
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if ( $_[1] eq 'access' ) {
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$^H &= ~$filetest::hint_bits;
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} else {
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die "filetest: the only implemented subpragma is 'access'.\n";
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}
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}
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1;
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